The present invention relates in general to the delivery of stents into a body lumen, such as a blood vessel, to maintain the patency thereof. More particularly, the present invention relates to an improved stent delivery system which can quickly and accurately position a self-expanding stent into a body lumen.
In a medical procedure known as percutaneous transluminal coronary angioplasty (PTCA), a balloon catheter is used to dilate the lumen of a coronary artery which has become narrowed or restricted due to the accumulation of atherosclerotic plaque along the artery wall. In the PTCA procedure, a balloon catheter is advanced through the vasculature to the stenosis and the balloon is inflated to radially compress the atherosclerotic plaque against the inside of the artery wall. The balloon is then deflated so that the dilation catheter can be removed and blood flow resumed through the dilated artery.
Occasionally, the inflation of the balloon within the artery lumen will dissect either the stenotic plaque or the intima of the blood vessel or both. After the balloon is deflated and removed, blood can flow between the arterial wall and the dissected lining thereby constricting the flow passage or causing a section of the dissected lining, commonly called an "intimal flap," to be forced into the flow passageway. In the event of partial or total occlusion of a coronary artery by a dissected arterial lining, the patient is put in an extremely dangerous situation requiring immediate medical attention, particularly when the occlusion occurs in one of the coronary arteries.
Another problem which frequently arises after an angioplasty procedure is the appearance of a restenosis at or near the site of the treated artery. The restenosis may appear due to the accumulation of additional atherosclerotic plaque or may be the result of weakened arterial walls which have collapsed inward to restrict blood flow. When restenosis appears, the treated patient may require an additional angioplasty procedure or other treatment such as by-pass surgery, if an additional angioplasty procedure is not warranted.
Due to the problems caused by dissections of the arterial lining or the appearance of restenosis, much research has been performed on ways to maintain the patency of an artery after the angioplasty procedure is completed. In recent years, expandable endoprosthetic devices, commonly called "stents," have gained widespread acceptance as a means to support the arterial walls and maintain the patency of a treated vessel. Stents are generally cylindrically shaped intravascular devices which are placed within a damaged artery to hold it open and maintain unimpeded blood flow. Stents prevent dissected arterial linings from occluding an artery by pressing the dissected tissue against the arterial wall until natural healing results in the re-securing of the dissected tissue to the arterial wall. Stents also prevent the appearance of restenosis in the treated vessel by supporting the weakened arterial walls.
Various means have been developed for delivering and implanting intravascular stents within a body lumen. One common method involves compressing or otherwise reducing the diameter of a self-expanding stent, mounting the compressed stent on the distal end of a delivery catheter, placing a tubular sheath over the stent to restrain the stent in the contracted condition, and advancing the catheter through the patient's vasculature to the desired location. Once the stent is properly positioned, the stent is exposed by withdrawing the sheath proximally with respect to the stent, advancing the stent distally with respect to the sheath, or performing a combination of both. Once free from the sheath, the self-expanding stent expands against the arterial walls to thereby hold open the artery or other body lumen into which it is placed.
Other examples of stent delivery systems include U.S. Pat. No. 5,026,377 to Burton et al. Burton discloses an instrument for the deployment or retraction of a self expanding stent in a body canal, which comprises an elongated tubular outer sleeve having disposed therein an elongated core which is moveable relative to the sleeve and has a grip member formed at or near its distal end, which grip member is adapted to releasably hold a self-expanding stent within the outer sleeve. U.S. Pat. No. 5,190,058 to Jones et al. discloses a method of using a temporary stent catheter. The catheter comprises a catheter tube having a distal end and a proximal end; an elongated balloon inflatable by fluid pressure attached to the catheter tube near its distal end; a stent having a tubular configuration attached to the catheter tube near its distal end and surrounding the balloon; a pressurization device near the proximal end of the catheter tube for inflating and deflating the balloon, whereby the stent may be pressed against the wall of a blood vessel by the balloon and the balloon may be subsequently deflated; a restriction device near the proximal end of the catheter tube for maintaining the stent in an expanded condition and for subsequently effecting the radial contraction of the stent whereby it may be removed from the blood vessel.
U.S. Pat. No. 5,201,757 to Heyn et al. discloses an apparatus for deploying a radially self-expanding stent that includes proximal and distal sleeves respectively containing proximal and distal end portions of the stent in a reduced radius delivery configuration. Once the stent and sleeves are positioned at the intended fixation site, the sleeves are moved axially with respect to one another to permit radial self-expansion of the stent only over its medial region, while the sleeves continue to contain the axially outward regions of the stent. Upon sufficient movement of the sleeves axially relative to one another, the stent becomes totally free of the sleeves. U.S. Pat. No. 5,290,295 to Querals et al. discloses a tool for the intraluminal insertion and deployment of a tubular graft within a blood vessel, which is constructed from a flexible insertion shaft with a tapered distal end, a tubular sheath, a deployment slider, and a safety locking tube.
U.S. Pat. No. 5,391,172 to Williams et al. discloses a stent delivery system with coaxial catheter handle. The catheter handle provides relative motion between the outer sheath of a stent delivery catheter and an underlying catheter, via a thumb switch, to enable the outer sheath to withdraw from over the underlying catheter and expose a vascular prosthesis.
U.S. Pat. No. 5,507,768 to Lau et al. discloses a stent delivery method and system that includes an elongated delivery sheath and a catheter disposed within an outer lumen of the sheath having an expandable member on its distal extremity. An expandable stent is mounted on the expandable member, the distal portion of the sheath tapers down and is tucked within an elastic cone during transport of the stent to a stenotic region. A manipulating device is provided on the proximal end of the delivery system to effect relative axial movement between the sheath and the catheter so as to expose the stent mounted on the expandable member on the catheter within a body lumen such as a coronary artery and allow the expansion of the stent by the expansion of the expandable member.
One of the difficulties with some prior art self-expanding stents involves deploying the stent at the precise, desired location within the body lumen. Typically, a self-expanding stent is mounted on the distal end of a delivery catheter which is attached to a manipulator handle outside the patient's body. The stent is deployed by actuating a mechanism on the manipulator handle, such as a thumb plate, which is hand operated by the physician. When the thumb plate is withdrawn proximally relative to the manipulator handle, the sheath is withdrawn proximally relative to the catheter and stent.
The problem arises when the operator applies a proximal force to move the thumb plate, a counteracting distal force is normally applied to the manipulator handle thereby making it very difficult to hold the manipulator handle steady. If the handle is inadvertently moved while the sheath is retracted, the stent may not be deployed in the desired location. As a result, the ends of the stent may damage the vessel by pushing into the vessel wall. In addition, a poorly placed stent may do more harm than good and can be very difficult to retrieve once deployed. Therefore, it is critical to position the stent accurately on the first attempt.
What has been needed and heretofore unavailable is a delivery system for self-expanding stents which provides a means to fix the position of the manipulator handle during the stent deployment process to prevent unwanted movement and to provide greater accuracy of stent placement within a body lumen. The present invention satisfies this need.